This sample chapter covers the different types of processor chips that have been used in personal computers since the first PC was introduced almost two decades ago. These sections provide a great deal of technical detail about these chips and explain why one type of CPU chip can do more work than another in a given period of time.

Microprocessors

The brain or engine of the PC is the processor (sometimes called
microprocessor), or central processing unit (CPU). The CPU performs the
system's calculating and processing. The processor is easily the most
expensive single component in the system, costing up to four or more times
greater than the motherboard it plugs into. Intel is generally credited with
creating the first microprocessor in 1971 with the introduction of a chip called
the 4004. Today Intel still has control over the processor market, at least for
PC systems. This means that all PC-compatible systems use either Intel
processors or Intel-compatible processors from a handful of competitors (such as
AMD or Cyrix).

Intel's dominance in the processor market had not always been assured.
Although Intel is generally credited with inventing the processor and
introducing the first one on the market, by the late 1970s the two most popular
processors for PCs were not from Intel (although one was a clone of an
Intel processor). Personal computers of that time primarily used the Z-80 by
Zilog and the 6502 by MOS Technologies. The Z-80 was noted for being an improved
and less expensive clone of the Intel 8080 processor, similar to the way
companies today such as AMD, Cyrix, IDT, and Rise Technologies have cloned
Intel's Pentium processors. In that case though, the clone had become more
popular than the original.

Back then I had a system containing both of those processors, consisting of a
1MHz (yes, that's 1, as in 1MHz!) 6502-based Apple main system with
a Microsoft Softcard (Z-80 card) plugged into one of the slots. The Softcard
contained a 2MHz Z-80 processor. This allowed me to run software for both types
of processors on the one system. The Z-80 was used in systems of the late 1970s
and early 1980s that ran the CP/M operating system, while the 6502 was best
known for its use in the early Apple computers (before the Mac).

The fate of both Intel and Microsoft was dramatically changed in 1981 when
IBM introduced the IBM PC, which was based on a 4.77MHz Intel 8088 processor
running the Microsoft Disk Operating System (MS-DOS) 1.0. Since that fateful
decision was made, PC-compatible systems have used a string of Intel or
Intel-compatible processors, each new one capable of running the software of the
processor before it, from the 8088 to the current Pentium III/Celeron and
Athlon/Duron. The following sections cover the different types of processor
chips that have been used in personal computers since the first PC was
introduced almost two decades ago. These sections provide a great deal of
technical detail about these chips and explain why one type of CPU chip can do
more work than another in a given period of time.